The therapeutic principle of a focused ultrasonic therapeutic system is to employ ultrasonic waves that are capable of going through the physical tissue and being focused within the tissue. Therefore, the ultrasonic beams are focused accurately at the diseased part of a patient and the instantaneous high temperature caused by focusing at a focal spot can cause coagulation necrosis of tissue within the targeted location, and the non-invasive therapy can be achieved. The imaging device such as MRI can quickly obtain the images of the internal body structures of a patient with high accuracy; therefore, the imaging device is always used together with an ultrasonic therapeutic system.
In a focused ultrasonic therapeutic system, the ultrasonic waves transmitted from the ultrasonic transducer are eventually focused at the targeted location through the couplant liquid. For an ultrasonic transducer with a fixed focal point, the movement of the focal point is realized by external moving locating mechanism, for example, the mechanical arm 7 shown in FIG. 1 and FIG. 2. As shown in FIG. 1 and FIG. 2, the ultrasonic therapeutic applicator 5 and some part of the mechanical arm 7 are located in the box 9 that contains couplant liquid 4. The mechanical arm 7 is seal-connected with the box 9 through a flexible joining unit 8. During treatment, when the mechanical arm 7 drives the focal point of ultrasonic therapeutic device to move within the target area, the level of couplant liquid in the box will vary accordingly. As shown in FIG. 1, when the ultrasonic therapeutic applicator 5 moves ΔX along the positive direction of X-axis, the level of couplant liquid in the box will change from H to H+ΔH1. As shown in FIG. 2, when the ultrasonic therapeutic applicator 5 moves ΔY along the positive direction of Y-axis, the level of couplant liquid in the box will change from H to H+ΔH2.
In the prior art, the flexible joining unit 8 sometimes adopts flexible telescopic sleeve. If the shape of telescopic sleeve is selected appropriately, when the ultrasonic therapeutic applicator moves in Y-direction, ΔH2=0 and the liquid level keeps unchanged; but when the ultrasonic therapeutic applicator moves in X-direction and when ΔX≠0, ΔH1≠0 and the liquid level varies.
When the imaging device is introduced with the ultrasonic therapeutic system, especially an MRI (Magnetic Resonance Imaging) apparatus, the level changes of couplant liquid will influence the imaging results of MRI and accordingly the diagnostic effect of MRI is influenced.
Therefore, it is very important for an ultrasonic therapeutic system guided by MRI to keep the level of couplant liquid unchanged.